1. Field of the Invention
This invention relates to a densified gas cleaning system, more particularly, to a fluid driven agitator used in densified gas cleaning system.
2. Description of the Related Art
Most of conventional industrial cleaning processes are wet cleaning types, which use solvents, water or aqueous solutions as cleaning media with addition of detergents. However, such wet cleaning types requires a subsequent drying step. Besides, toxic contaminants and detergents are dissolved in water or solvents, which need to be treated before drainage. Nowadays, the gradually stringent provisions for environmental protection progressively ban the use of conventional solvents due to the air pollution, ozone depletion, and greenhouse effect resulted from the use of such solvents. Moreover, large consumption of fresh water and energy along with the wastewater treatment also increase the cost of cleaning.
In the past twenty years, several liquefied gases have been found owning solvent-like solubility in the supercritical state and can be used to replace the conventional solvents for use in extracting or cleaning. Among theses gases, carbon dioxide, which has advantages of environmental benign, safe, low cost, and pollution-free, is one of the most frequently used gas applied in commercialized equipments.
Densified fluid for cleaning may either be liquefied gas in its liquid state or supercritical state. Conventional auxiliary cleaning apparatus such as ultrasonic generators, nozzles, agitators, or UV radiation devices as disclosed in U.S. Pat. Nos. 5,068,040, 5,316,591, 5,370,740, 5,337,446, 5,377,705, 5,456,759, and 5,522,938 can be added to enhance the cleaning effect when using liquid phase fluids for cleaning. U.S. Pat. Nos. 4,944,837, 5,013,366, 5,267,455, 5,355,901, 5,370,742, and 5,401,322 disclose that the contaminants are dissolved and removed away from the surface of articles due to the low surface tension and strong solubility properties offered by the supercritical fluids.
The conventional densified gas (such as supercritical or liquid carbon dioxide) cleaning system having an agitator is often a magnetically coupled type as described in U.S. Pat. No. 5,267,455 or a penetrating shaft type as described in U.S. Pat. Nos. 5,337,446, 5,355,901, 5,377,705, and 5,881,577. A shaft of a penetrating shaft agitator penetrates a sidewall of a vessel to join a driving motor. Hence, the shaft is complicated in design to anticipate leakage prevention. Furthermore, the short life-span of a rotary seal requires periodical replacement, especially for one operated under high pressure. To avoid the defects mentioned above, a magnetically coupled agitator is applied broadly because it has the advantages of reducing labor, easily assembling, and leakage-free. On the other hand, the cost of manufacturing the magnetically coupled agitator is very high. A spraying flow type is also utilized for agitation, wherein several nozzles mounted on an inner sidewall of a pressure vessel blow towards a rotary basket along a tangent direction, as disclosed in U.S. Pat. No. 5,669,251, or blow towards a turbine wheel mounted on the rotary basket to drive rotation, as disclosed in U.S. Pat. No. 6,098,430. Although the spraying flow type has the advantages of simple structure and low cost, it can only be applied in a system with a rotary basket, but not one with a fixed basket or one without a rotary basket.
To eliminate the defects mentioned above, a fluid driven agitator used in densified gas cleaning system is provided to overcome the problems of complicated structure for preventing leakage, the short life-span of seal happened in the conventional penetrating shaft type, and the cost and difficulty in downsizing for the magnetically coupled type agitator.